Spontaneous Mutations

Missense mutation

"different amino acid" - resulting protein may only partially function - termed "leaky" - a single base substiution that changes codon for one amino acid into codon for another amino acid

Silent mutations

"wild-type amino acid" - used to indicate mutation that does not alter protein function - change nucleotide sequence of codon, but not the encoded amino acid

Radiation

- UV - Xrays

Larger mutations

- less common - change in a single base pair - insertions, deletions, inversions, duplication, and translocations of nucleotide sequences

Point mutations

- most commun - from alteration of single pairs of nucleotide - from addition or deletion of nucleotide pairs

Spontaneous Mutations

- occur during replication - happen at a low rate - just a single base pair change in a genetic code can have significant effect on cell

Nonsense mutation

- specifies stop codon, yield shorter protein - converts a sense codon to a stop codon

Transition mutations

AT to GC

Transversion mutations

CG to GC

Alkylating agents

add alkyl groups onto nucleases - nitrosoguanidine adds methyl group to guanine - base pairs with thymine base analogs resemble nucleobases - 5-bromouracil resembles thymine - 2-amino purine resembles adenine

Mutagen

an agent that induces change

Intercalating agents

cause frameshift mutations

X rays

cause single and double strand breaks in DNA - double strand breaks often produce lethal deletions

Nitrous acid effect

changes cytosine to uracil and pairs with adenine instead of guanine

Ethidium bromide

common intercalating agents - likely carcinogen

Conditional mutations

expressed only under certain environmental conditions

UV irradiations

forms thymine dimers - covalent bonds between adjacent thymines - cannot fit into double helix, distorts molecule - replication and transformation stall - mutations results from cell's SOS repair mech.

Flat intercalating molecules

insert between adjacent base pairs in DNA strand and push nucleotides apart, causing errors during replication

Conditional lac operon mutants

map in the operator site and produce altered operator sequences not recognized by repressor - operon is always transcribed and b-galactosidase is always synthesized

Chemical mutations

may cause base substitutions or frameshift mutations

Combination therapy

multiple antibiotics is often used; unlikely cells will simultaneously develop resistance

Mutation rate

probability of mutation each cell division typically between 10^-4 and 10^-12 for a given gene

Mutations in tRNA and rRNA

protein synthesis is always disrupted

Inducted mutations

result form outside influence

Frameshift mutation

results from insertion of deletion of one or two base pairs in the coding region of the gene - impact depends on number of nucleotides and location within protein - three pairs changes on codon - one or two pairs yield mutation - often results in premature stop codon

Mutations can be ____ or ______

spontaneous or induced

Auxotrophic mutant

unable to make an essential macromolecule such as an amino acid or nucleotide - has a conditional phenotype - wile-type strain from which it arose is called prototroph

Chloroquine

used to treat malaria

Reversion

when bacteria change to their original state